cc @SomeoneToIgnore

## Summary

Follow-up to https://github.com/zed-industries/zed/discussions/55352,
where the conclusion was to split `editor.rs` incrementally by topic
instead of all at once.

This mechanically extracts editor config and reflow-related code into
`crates/editor/src/config.rs` and `crates/editor/src/rewrap.rs`, while
preserving existing behavior and keeping externally-used APIs public
where needed.

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A